From the Beach Boys' song "Kokomo," is there really a "Kokomo" out there?

Yes there really is a Kokomo Island. The island named Kokomo came AFTER the song though!

https://en.wikipedia.org/wiki/Kokomo_Island

Kokomo Island is part of the privately owned Sandals Royal Caribbean vacation resort in Montego Bay, Jamaica. It became famous after as the inspiration for the song Kokomo, written by Mike Love and performed by The Beach Boys. It is a very small island, and according to the Sandals Royal Caribbean website, the only amenities on the island are an Indonesian restaurant, a swimming pool, a jacuzzi, and a bar. The island caters to couples on tropical getaways.

There's also a Kokomo, Indiana, but I doubt that's what they were singing about.

Yes the Kokomo in the Beach Boys' song DOES exist in the Florida Keys. It is a resort area on the island of Islamorada about 25 miles south of Key Largo. Kokomo was written by John Phillips of the Mamas and Pappas for the Beach boys from a visit he actually made to Kokomo. Anyone visiting Kokomo will immediatly discover, near the Tiki Hut Bar, the thing what inspired the idea for the song. But you'll have to see it to understand how the song came about.
songplaces.com/Kokomo/Islamorada_Florida no longer exists

In its heyday, the Holiday Isle Resort had a poolside bar called Kokomo. The owner at the time created the bar after hearing inquiries from tourists looking for Kokomo. The bar was former a birdhouse, according to the resort. A sign at the bar plotted the distance to all the places referenced in the song, Hull said. Aruba, Jamaica, Bermuda, Bahama, Key Largo, Montego. Although the resort is now the Postcard Inn Beach Resort and Marina (home to the mid Keys Starbucks before the last two in Key West), people still make the connection between Kokomo and Islamorada. The resort has a re-imagined pool bar called Kokomo that serves cocktails, beer and wine and light fare from nachos to sandwiches.

Farther south, as in the end of the continental U.S., there was also a “Kokomo Beach.” Casa Marina Resort in Key West renamed their beach to reflect the song, along with a cocktail called “The Kokomo” for drinking by the beach and pool. Although the 1,100-foot private beach is no longer called Kokomo, the song still carries an association with the Keys, said Maureen Holden, a spokeswoman for Casa Marina, a Waldorf Astoria resort ...

“Kokomo was a name that originated with John Phillips of the Mamas and the Papas,” Love told the publication. “Phillips wrote the melody and the verse, and I wrote the chorus, and our friend Terry Melcher produced the record, and he came up with the ‘Oooh I want to take you…’ and it was a true collaboration.” Although Phillips pictured Kokomo as a place off the Florida Keys, there really is no Kokomo in South Florida. There is a Kokomo Charters in Sarasota, a Kokomo city in Indiana, a Kokomo in the Fiji Islands and a community named Kokomo in Hawaii. But the music video was filmed in Florida. The Beach Boys, with actor John Stamos on bongos, shot the video at The Grand Floridian before it officially opened.

https://www.sun-sentinel.com/travel/fl-fea-florida-keys-kokomo-beach-boys-20190920-fjl2o4qmqfblrbh56zx2kglwfm-story.html